In recent years, an organic EL device has attracted attention as a light-emitting device that can emit light with high luminance through low-voltage DC drive.
However, the organic EL device has a problem in that emission properties (e.g., luminance, luminous efficiency, and luminous uniformity) easily deteriorate with the passage of time.
It is considered that a deterioration in emission properties occurs when oxygen, water, and the like enter the organic EL device, and cause the electrode and the organic layer to deteriorate. Methods that utilize a sealing material have been proposed in order to solve this problem. For example, Patent Document 1 discloses an organic EL device having a configuration in which a transparent electrode, a hole-transporting layer, an organic EL layer, and a bottom electrode are sequentially stacked on a glass substrate, and a non-water-permeable glass substrate is secured thereon through a photocurable resin layer that exhibits humidity resistance. Patent Document 2 discloses a method that seals an organic EL device using a sealing film that is formed using a moisture-proof polymer film and an adhesive layer.
An acrylic-based adhesive and an acrylic-based pressure-sensitive adhesive (hereinafter referred to as “acrylic-based adhesive and the like”) have been known as an adhesive and a pressure-sensitive adhesive that are used as the sealing material for the organic EL device, taking account of optical properties such as transparency. For example, Patent Document 3 discloses a UV-curable acrylic-based adhesive that can be cured at room temperature as a sealing material for an organic EL display. Patent Document 4 discloses an acrylic-based pressure-sensitive adhesive as a pressure-sensitive adhesive that can form a pressure-sensitive adhesive layer that maintains transparency even when subjected to a heat treatment and a drying treatment that are performed when producing the organic EL device in order to remove water and the like.
However, a sealing material that is formed using the acrylic-based adhesive and the like has an insufficient water barrier capability, and is not suitable as a sealing material for which a very high water barrier capability is required (e.g., the sealing material for the organic EL device). When a sealing material that is formed using the acrylic-based adhesive and the like has a crosslinked structure, the sealing material may be easily delaminated from the adherend due to an impact, vibrations, heat, or the like, and the water barrier capability may deteriorate to a large extent.
In recent years, an adhesive that includes a polyisobutylene-based resin has been proposed as a sealing adhesive that exhibits a good water barrier capability. For example, Patent Document 5 discloses an adhesive composition that is used as a sealing material for an organic EL display, and includes a specific hydrogenated cycloolefin-based polymer and a polyisobutylene resin.